Gravity and friction operated back-stop mechanism



Aug. 31, 1954 P. v. WHITNEY GRAVITY AND FRICTION OPERATED BACK-STOP MECHANISM Filed Aug. 19, 1952 mmvrox: u L \l WHITN E Patented Aug. 31, 1954 2,687,785 I C E GRAVITY AND FRICTION OPERATED BACK-STOP MECHANISM Paul V. Whitney, Columbus, Ohio, assignor to The J eifrey notation of Ohio Manufacturing Company, a. cor- Application August 19, 1952, Serial No. 305,255

4 Claims. 1

This invention relates to back-stop mechanisms, and more particularly, to an improved back-stop mechanism that may be employed with particular advantage for arresting reverse operation of machinery preferably, but not necessarily, by being applied to a shaft thereof.

An object of the invention is to provide an improved back-stop mechanism of the type set forth that includes a ratchet wheel, a dog that engages the ratchet wheel for arresting rotation of it in one direction, and a dog operating mechanism that holds the dog out of engagement with the ratchet wheel rotated in the other direction and which permits or causes the dog toengage the ratchet wheel when it is rotated in the said one direction.

Other objects of the invention will appear hereinafter the novel features and combinations being set forth in the appended claims.

In the drawing:

Fig. 1 is a view in side elevation of the top portion of a. chain and bucket elevator showing the back-stop apparatus of this invention applied to the head shaft of the elevator;

Fig. 2 is a side view in elevation on a larger scale of the back-stop mechanism seen in Fig. 1, with a portion of the elevator member supporting it being shown;

Fig. 3 is a view in plan of the back-stop mechanism seen in Fig. 2 with portions broken away to show certain of its internal features of construction;

Fig. 4 is a fragmentary view of the back-stop mechanism embodying the invention and including a resilient mounting means for the ratchet wheel engaging dog; and

Fig. 5 is a View in section, the section being taken substantially on line 5--5 of Fig. 4.

. In Fig. l of the drawing there is shown the top, head or discharge portion of a chain and bucket elevator iii. Elevator Iii includes a frame having four spaced upright side angle members II and a plurality of cross-members, one of which is indicated at I2. At the top of the upright members ii there are two spaced horizontally extending frame members It that form the base of a platform i4 located at one side of the casing [5 of the elevator head portion. Plat form I4 supports an electric motor and speed reducing gear mechanism l 6 which drives the head shaft ll of elevator l through a sprocket I8 mounted on the driven shaft of the motor and speed reducing gear apparatus IS, a chain It, and a large sprocket wheel 2!] mountedupon and keyed to the head shaft I 1. The head shaft I! is supported adjacent each of its ends by a suitable bearing, not shown, each of which is mounted upon one of the horizontally extending frame members I3. Head shaft l1 extends transversely and generally horizontally through the casing l5, and within the casing it carwhen the latter is a ries a. pair of spaced wheels or. sprockets 2| over which spaced chains, one of which is seen at 22,

of a chain and bucket conveyer, travel and are driven. In the operation of elevator It material which is conveyed upwardly by the buckets 23 of the conveyer is discharged over the wheels or sprockets 2| and passes from the casing I5 through a. discharge chute 24 formed at one side of the casing [5. It is imperative in apparatus such as the elevator Ill, described in part above, that a mechanism be provided that will positively prevent reverse rotation of the elevator when its operating motor is de-energized. The back-stop mechanism of this invention is shown associated with head shaft ll of this elevator and it may be used with particular advantage for preventing or arresting the above mentioned reverse rotation or motion of the elevator.

Referring now to Figs. 1, 2 and 3 of the drawings, and more particularly, to Figs. 2 and 3 thereof, the back-stop mechanism includes a ratchet wheel 25 that may be pressed upon and keyed, or otherwise suitably secured, to one end of the head shaft ll of elevator l0 so that it may partake of any rotary motion of the head shaft II. The ratchet wheel 25 is serrated throughout its entire outer periphery to form teeth 26 which, in general, resemble those of a saw. At each of its opposite sides the ratchet wheel 25 is machined to form a cylindrical friction surface or drum 2'! (see particularly Fig. 3) A dog 28 is mounted for pivotal swinging movement about a horizontal axis positioned lateral- 1y of and extending parallel to the axis of rotation of the ratchet wheel 25 and it is positioned so as to engage the teeth 26 of the latter for preventing rotation of both the ratchet wheel 25 and the shaft I! in a clockwise direction as viewed in Fig. 2 of the drawings. Dog 28 is mounted for pivotal movement about the axis of a stainless steel bolt29 and nut 30 carried by a bracket or lug 3| bolted directly upon the top of one of the frame members [3 by bolts and nuts 32. The shape of the dog 28 is such that when it as viewed in Figs. 1 and 2 nose 33 ratchet wheel 25 to prevent rotation of the latter in a clockwise direction. Dog 28 forms a cam slot 34 that extends transversely through it and lies in a. plane that extends parallel to the axis of rotation of the head shaft I! and slopes upwardly toward the ratchet wheel 25. Dog 28 is held out of engagement with the ratchet wheel 25 when the latter rotates in a counterclockwise direction, as seen in Figs. 1 and 2 of the of the drawings, its

. drawings and it is moved into engagement aforesaid, includes a frame or cage 35 formed of d a pair of identical but reversely positioned side is rotated or swung counterclockwise,

will engage one of the teeth 28 of the,

members 35 spaced one on eachside of the ratchet wheel and connected by bolts 31 and spacers 33. Each side member 36 includes a hub having a bore 39 (see Fig. 3) that surrounds one of the cylindrical friction surfaces or drums 21- of the ratchet wheel 25. Interposed between the bore 39 and each side member 36 and each of the cylindrical friction surfaces 21 is a wearing ring or lining 43 which may be made of any material, such for example, as an asbestos brake lining material, brass, babbitt, or any other suitable wear resistant friction substance, and this wearing ring of friction material til is retained in position between the bore 39 and the cylindrical friction surface 21 by a shoulder or cylindrical radially inwardly projecting abutment ll that overlaps a cylindrical peripheral shoulder 42 formed at the side of the cylindrical surface 21 ofthe ratchet wheel 25' and a radial shoulder 13 formed on the ratchet wheel 25 against which the innermost edge of the liner is, as well as a shoulder or boss [A l of the side member abuts. The wearing ring 43 functions to a slight degree as a brake or friction band and it preferably floats in the bore 39 and. on the friction surface 21, that is, it is not anchored and it is held in its proper position by the shoulders ti and 33, as previously mentioned.

The side members 35 together with bolts 31 and spacers 38 form, in eifect, a cage that is carried by the ratchet wheel 25 through the cylindrical friction surfaces 21 of the latter and this cage normally tends to rotate with the ratchet wheel 25 by reason of friction created between the surfaces 21 and 33 and the ring or band ii! of friction material. One of the bolts 31' and spacers 33 extend between the operating arms 45 of the members 36 through the cam slot 33 in the dog 28. It will be seen that when the cage 35, including the side members 35, bolts 31 and spacers 33 is rotated by the ratchet wheel 25 in a clockwise direction, as seen in Figs. 1 and 2 of the drawings, that the bolt 31 and spacer 38 in the cam slot 34. of dog 28 will cooperate with the cam slot 3 3 to cause the dog 23 to be swung or rotated counter-clockwise about the horizontal axis of its mounting bolt 29 to draw positively the nose 33 of the dog 28 into engagement with a tooth 25 of the ratchet wheel. it will also be seen that when the nose 33 of dog 28 is engaged with one of the teeth at of ratchet wheel 25' and the ratchet wheel 25 is started to rotate in a counter-clockwise direction that the tooth 26 immediately below and engaging the nose 33 of dog 28 will operate to cam or rotate the dog 28 in a clockwise direction. This action of the dog 23, of course, assists the floating cage 35 in starting to rotate with or follow the motion of the ratchet wheel 25. Continued rotation of the cage 35 causes the dog to become completely disengaged from the periperal tooth 25 of the ratchet wheel 25 as the latter continues to rotate in a counterclockwise direction as seen in Figs. 1 and 2 of the drawings.

It is important to note that the side members 33, as seen in Fig. 2 of the drawings, are symmetrical about a vertical plane passing through the horizontal axis of rotation of the shaft 11 and the ratchet wheel 25 and they are made symmetrical for two reasons, namely, so that in the manufacture of the unit two identical castingsmay be employed to form opposite sides of the cage 35 and to provide counterbalance arms 46 which together with the bolt 31 and spacer 38' that interconnect the opposite arms of the cage 35 will substantially counterbalance the operating arms 45 and the bolt 31 and spacer 38 that interconnects them and extends through the cam slot 34 in the dog 28. The arms 35 and 36 are positioned above a horizontal plane passing through the axis of rotation of the shaft i1 and ratchet wheel 25 so as to offset the center of gravity, as indicated at 41 in Fig. 2 of the drawings, from said axis of rotation and so that when the cage 35 is in the position shown wherein the dog 28 is being held away from the ratchet wheel 25, the center of gravity of the cage 35 lies substantially in or adjacent a vertical plane passing through said axis of rotation of shaft 51 and ratchet wheel 25. In other words, the cage is so counterbalanced by its arms 43, and interconnecting bolts 31 and spacer 33, that when it. is occupying the position seen in Fig. 2 of the drawings, its center of gravity 41 is above the axis of rotation of the shaft 11 and ratchet wheel. 25 or, in or adjacent a vertical plane intersecting the latter, and, therefore, the cage 35 is substantially balanced with respect to the axis of rotation of the ratchet wheel when the dog is being held disengaged from the ratchet wheel 23 by the cage 35.

It will be seen that when the ratchet wheel is rotated in a counter-clockwise direction, as viewed in Fig. 2 of the drawings, and above described, that cam slot 3t in dog 28 acts upon the bolt 31 and spacer 38 to hold the cage in the substantially balanced position described and that whenever reverse rotation, or rotation in a counterclockwise direction as shown in Fig. 2 occurs the cage 35, by reason of its own weight, will create sufficient friction between the bores 39, the friction bands t0 and the spaced cylindrical surfaces 21 to cause the cage to follow the reverse rotation of the latter. The cage 35 is easily unbalanced by reverse rotation of the ratchet wheel and upon rotating reversely with it its operating arms 45 acting through the interconnecting bolt 31 and spacer 38 cooperate with the cam slot 34 to cause the dog to be cammed rapidly and positively into engagement with one of the teeth 26.

In Figs. 4 and 5 of the drawings there is shown a modified mechanism in which a dog 5%], having the identical function of dog 23, is mounted through a stainless steel bolt 5| between a pair of generally horizontally extending arms 52 mounted upon a cross bolt 53 and spaced apart by a spacer 54. Arms-52 rest upon a bed assembly that includes a plate 55, a resilient pad or cushion 53 and a base member 51 that are secured together by a pair of bolts and nuts 58. Base member '51 is bolted upon one of the members 13, as is the bracket 3 I and it is provided with a pair of spaced upstanding ears as through which the bolt 53 that carries the spaced arms 52 extends. Arms 5:52 are each provided with a downwardly extending lug fill that engages a shoulder 5! on each of the ears 52 of base member 51, for preventing arms 52 from rotating clockwise as viewed in Fig. 4 of the drawings, or away from the plate The resilient mounting of the dog 50, shown in Figs. i and 5 of the drawings, is particularly useful in a back-stop apparatus wherein the diameter of the ratchet wheel 62 is relatively large, and wherein the shaft, when it reverses its direction of rotation, is heavily loaded because when the dog is swung against the ratchet wheel and engages one of the teeth thereof, a portion of the shock created by stopping the reverse rotation' of the ratchet wheel is cushioned by means of: the. resilient pad 56*.

From the foregoing description it will be read ily apparent that the back-stop mechanism is capable of and does actually operate by reason of friction created solely by the weight of the operat ing cage 35 riding upon the spaced cylindrical surfaces 2'? of the ratchet wheel and it may be stated that the band. of friction material 40 is employed more for the purpose of its Wear resistant qualities or longevity than for its friction qualities and this because long life of the wearing ring 443 is desirable. Because the operating cage is substantially balanced, very little rotative eifort, and consequently, friction is required to cause the cage 35 to follow or rotate with the friction surfaces or drums 2'! of the ratchet wheel 25.

Obviously those skilled in the art may make various changes in the details and arrangement of parts without departing from the spirit and scope of the invention as defined by the claims hereto appended and applicant wishes therefore not to be restricted to the precise construction herein disclosed.

Having thus described and shown an embodiment of the invention, what it is desired to secure by Letters Patent of the United States is:

l. A gravity and friction operated back-stop mechanism including a ratchet wheel adapted to rotate on a generally horizontal axis having means forming a pair of cylindrical friction surfaces spaced one at each side thereof, a dog, means for mounting said dog for swinging movement about an axis extending parallel to said axis of rotation of said wheel, dog operating means for holding the dog away from said ratchet wheel when the latter is rotated in one direction and for causing the dog to swing against the ratchet wheel upon rotation of the latter in the reverse direction, said dog operating means including a cage having a pair of substantially identical side members spaced one at each side of said ratchet wheel, each of said members including a hub surrounding one of said cylindrical friction surfaces and a shoulder, a readily replaceable band of wearable material interposed between said bore and said cylindrical friction surface and abutting said shoulder, each of said members also including a laterally extending arm for operating said dog and a laterally extending counterbalance arm, bolt and spacer means interconnecting the counterbalance arms, and bolt and spacer means interconnecting the dog operating arms, said cage having a center of gravity offset from the axis of rotation of said ratchet wheel and lying substantially directly thereabove when said dog is swung away from said ratchet wheel whereby said dog operating means is sub stantially balanced and whereby it is easily unbalanced by friction created by its own weight when said ratchet wheel is rotated in said reverse direction.

2. A gravity and friction operated back-stop mechanism including a ratchet wheel adapted to rotate on a generally horizontal axis having means forming a pair of cylindrical friction surfaces spaced one at each side thereof, a dog, means for mounting said dog for swinging movement about an axis extending parallel to said axis of rotation of said wheel, dog operating means for holding the dog away from said ratchet wheel when the latter is rotated in one direction and for causing the dog to swing against the ratchet wheel upon rotation of the latter in the reverse direction, said dog operating means including a cage having a pair of substantially identical side members spaced one at each side of said ratchet wheel, each of said members ineluding a hub surrounding one of said cylindrical friction surfaces, a readily replaceable band of wearable material interposed between said bore and said cylindrical friction surface, each of said members also including a laterally extending arm for operating said dog and a laterally extending counterbalance arm, 'bolt and spacer means interconnecting the counterbalance arms, and bolt and spacer means interconnecting the dog operating arms, said cage having a center of gravity offset from the axis of rotation of said ratchet wheel and lying substantially directly thereabove when said dog is swung away from said ratchet wheel whereby said dog operating means is substantially balanced and whereby it is easily unbalanced by friction created by its own weight when said ratchet wheel is rotated in said reverse direction, i

3. A gravity and friction operated back-stop mechanism including a ratchet wheel adapted to rotate on a generally horizontal axis having means forming a cylindrical friction surface adapted to rotate therewith, a dog, means for mounting said dog for swinging movement about an axis extending parallel to said axis of rotation of said wheel, dog operating means for holding the dog away from said ratchet wheel when the latter is rotated in one direction and for causing the dog to swing against the ratchet wheel upon rotation of the latter in the reverse direction, said dog operating means including a member having a hub surrounding sai cylindrical friction surface, a band of friction material interposed between said bore and said cylindrical friction surface, said member also being counterbalanced and having its center of gravity offset from the axis of rotation of said ratchet wheel and lying substantially directly thereabove when said dog is swung away from said ratchet wheel whereby said dog operating member is substantially balanced and wherebyit is easily unbalanced by friction created by its own weight when said ratchet wheel is rotated in said reverse direction.

4. A gravity and friction operated back-stop mechanism including a ratchet wheel adapted to rotate on a generally horizontal axis having means forming a cylindrical friction surface adapted to rotate therewith, a dog, means for mounting said dog for swinging movement about an axis extending parallel to said axis of rotation of said wheel, dog operating means for holding the dog away from said ratchet wheel when the latter is rotated in one direction and for causing the dog to swing against the ratchet wheel upon rotation of the latter in the reverse direction, said dog operating means including a member having a hub surrounding said cylindrical friction surface, said member also being counterbalanced and having its center of gravity offset from the axis of rotation of said ratchet wheel and lying substantially directly thereabove when said dog is swung away from said ratchet References Cited in the file of this patent UNITED STATES PATENTS Name Date Rhoacles July 27, 1920 Moody Apr. 14, 1936 Number wheel whereby said dog operating member is substantially bal-' 

